The invention relates to a process for coating foil comprised of nickel or a nickel alloy and to a coated foil comprised of nickel or a nickel alloy. Coated foils of this type are preferably laterally textured and are used in particular as shaving foils for electric razors.
Shaving foils of this type and other products based on nickel foils are generally produced by electrodeposition. Various process variants make it possible to produce both lateral texturing with apertures and projecting parts which form a shaving edge.
Recently, for various reasons, it has been attempted to enable these foils, which are exchangeable, to be recognized visually and to be marked in such a way that there is no risk of confusion, since their application areas differ.
It is known for a metal layer which is from 2.5 to 3 xcexcm thick to be applied to a nickel foil. Then, this layer is converted into an oxide or hydroxide by anodization or in a plasma (JP 610 648 72-A). This has the drawback that the process is relatively complicated and the bonding strength of the layer is low. Only a few colours of layers can be produced, and the cutting properties are impaired by a layer of this type in the thickness indicated.
It is also known for coloured layers to be produced on cutting tools and razor blades by dipping and electrodeposition treatment of steel materials in chromic acid and sulphuric acid (GB 1,407,407; U.S. Pat. No. 5,528,833; DE 21 26 129 A1; DE 22 30 157; AT 304,996). A drawback is that the deposition of such layers requires ferritic and austenitic steels and treatment temperatures of approximately 300 to 700xc2x0 C., and consequently these processes cannot be transferred to thin nickel foils.
It is also known for a sublayer of electrodeposited copper and a further metallic layer to be applied to razor blades in order to visually indicate wear and therefore the end of the service life of razor blades (DE 35 33 238). However, it is not possible in this way to produce different layer colours, and layers of this nature also fail to satisfy all the other requirements referred to above, apart from the indication of the level of wear.
Furthermore, it is known for visible marks or organic oxidation indicators of variable colour to be applied to razor blades in order to indicate the wear and therefore the end of the service life of razor blades (U.S. Pat. Nos. 3,879,844; 5,603,161). However, it is not possible in this way to produce a plurality of coatings which can be readily distinguished despite their range of colours, or to satisfy the other requirements which are imposed on such layers as described above.
Furthermore, it is known for various coatings to be applied to cutting tools, in particular to razor foils or shaving foils, so that the cutting properties and the service life are increased. These films have a thickness of from 0.1 to 1 xcexcm, consist of nitrides or carbides of the metals Ti, W or Cr, and are deposited by sputter ion plating or ion plating. For this purpose, a DC glow discharge at 300xc2x0 C. is provided (GB 2,123,039 A). These compounds may also be coloured, e.g. by golden titanium nitride. However, the abovementioned processes and coating materials cannot be used for the coating of electrodeposited nickel foils, since the electrodeposition production process and a low content of additive materials, e.g. sulphur, mean that the nickel foils may only be heated to at most 100xc2x0 C. while the coating is being applied. Otherwise, the foils become brittle, leading to them becoming unusable. Another drawback is the small number and low brilliance of the coloured films which can be produced.
It is also known for films to be applied by physical vapour deposition from nitrides or carbides of the fourth and sixth subgroups of the Periodic System of the Elements, leading to hard, coloured coatings with a thickness of from 0.1 to 1 xcexcm. These films are, for example, gold-coloured and have the same deficiencies when used for coating nickel shaving foils (DE 34 31 330 A1).
To avoid the drawbacks of the known processes, it is known to apply a high-function film with a high hardness and an adjustable colour to cutting tools, e.g. razors, which are produced by reactive vapour deposition in vacuo at a pressure of 10xe2x88x925 to 10xe2x88x924 mbar. In the process, metal oxynitrides, especially of the metals titanium or zirconium, are deposited. The metal vapour is generated in a high-vacuum evaporator or by means of ion sources. A film thickness mentioned is 0.3 xcexcm. This relates to the natural colour of the films formed, but the possibility of generating interference colours is also pointed out (U.S. Pat. No. 5,458,928). However, films which are applied in this way, in particular those with a thickness of around 0.3 xcexcm, reduce the sharpness of the cutting edges. Furthermore, it is very difficult to use the known processes to obtain a predetermined thickness and a high level of uniformity of the coating. Consequently, a high proportion of nickel foils of differing colour is produced, or else it is necessary to restrict oneself to the use of the body colour of such films. Furthermore, it has been found that the amount of heat introduced during the coating operation, owing to the high enthalpy of formation of the proposed zirconium and titanium compounds, is too high for coating thin nickel foils. Foils with a total thickness of 40 to 55 xcexcm, as are frequently used, therefore cannot be coated by these processes without becoming brittle.
Overall, it can be concluded that the known processes for producing shaving foils do not provide an optimum solution. The principal requirements of such shaving foils, such as visual marking so that there can be no confusion, differentiated use for different skin types or body parts, decorative and aesthetically pleasing design, prevention of nickel allergies on contact with the skin and a long service life are not fulfilled by any of the known processes.
The invention is based on the object of providing a process for coating foil comprised of nickel or a nickel alloy, and of providing a coated foil comprised of nickel or a nickel alloy, preferably a shaving foil for electric razors, which has a wear-resistant layer which can be produced in any desired colour and has a good adhesive strength and a very low thickness. There is also the special requirement that the colour tolerances are to be very low and the colour uniformity is to be very high. The process is to be highly productive and economical, i.e. capable of automation. A significant part of the object consists in enabling the coating to take place without imposing excessive thermal loads on the foils, even if the thickness of the foils is only 40 xcexcm or less. A further object of the invention is to provide foils with an indicator of the service life under abrasive load, in particular when used for electric razors, which are distinguished by the fact that this indicator can be adjusted to a predetermined range of values.
According to the invention, the object is achieved using the process according to claim 1. Claims 2 to 7 describe expedient embodiments of the process. A foil which has been coated according to the invention is described in claim 8.